Regulation of adaptive immunity

6 important questions on Regulation of adaptive immunity

Complexity of the adaptive immune system

- lies in the regulation of which cells to attack
- It has to ignore normal tissue
- tolerance = When the immunesystem does not respond to an antigen
- central tolerance = immature self-reactive lymphocytes die or alter their receptor specificity 
- peripheral tolerance = Mature lymphocytes that encounter self-antigens die, are turned off, or are supressed by Treg cells
- T cells can quickly become tolerant and stay that way for 100 days
- B cells take 10 days and only stay tolerant for up tot 50 days

B cell tolerance

- B cell antibody diversity is generated in two phases
- If receptor editing fails to generate a non-self-reactive B cell -> it will die
- Self reactive B cells will not make autoantibodies if APCs and T cells are absent or if Treg are present
- Administration of proteins can induce tolerance
- High doses induce anergy -> low doses induce Treg cell development  

B cell tolerance II

- The duration of tolerance depends on the persistence of an antigen
- Without the antigen tolerance fades
- prolonged response to an antigen occurs when the stimulus persists -> antigen that are rarely found in lymphoid tissues fail te induce a response
- antibodies suppress B cell responses
- specific antibodies can suppress a specific immune response
- IgG suppresses IgG and IgM
- IgM only suppresses IgM
- inhibitory receptors are very important in stopping activity of lymphocytes once they have completed their task -> they prevent inappropriate immune repsonses
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Regulation by the innate immune system

- Th17
  • host defence
  • induce acute inflammation
  • abundant in mucosal surfaces
- Interleukin-17
  • development of autoimmunity
  • inflammation
  • tumors
  • stimulate cells to produce proinflammatory molecules
  • regulates neutrophil accumulation
- M2 cells 

  • tolerance induction
  • suppress inflammation
  • participate in tissue repair
  • inhibit unwanted inflammatory reactions
- M1 cells
  • proinflammatory
- IDO (indoleamine2,3-dioxygenase)
  • inhibits T cell activation
  • proliferation
  • survival
  • depletion of tryptophan -> prevents growth in bacteria

Neural regulation of immunity

- Neuroendocrine hormones and neurotransmitters act on cells of the immune system + regulate cytokine balans
- Cytokines + chemokines act on the central nervous system as well

Hypothalamic-pituitary-adrenal cortical axis

- glucocorticoids suppress T cell function
- ACTH (adrenocorticotropic hormone) controls cortisol release

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